-Virtual testbeds are created dynamically whenever a verification job is\r
-started triggered by the patch submission to gerrit and destroyed upon\r
-completion of all functional tests. During test execution, all nodes are\r
-reachable thru the MGMT network connected to every node via dedicated NICs and\r
-links (not shown above for clarity). Each node is a Virtual Machine and each\r
-connection that is drawn on the diagram is available for use in any test case.\r
+SUT1 and SUT2 are two VMs (Ubuntu or Centos, depending on the test suite), TG\r
+is a Traffic Generator (TG, another Ubuntu VM). SUTs run VPP SW application in\r
+Linux user-mode as a Device Under Test (DUT) within the VM. TG runs Scapy SW\r
+application as a packet Traffic Generator. Logical connectivity between SUTs\r
+and to TG is provided using virtual NICs using VMs' virtio driver.\r
+\r
+Virtual testbeds are created on-demand whenever a verification job is started\r
+(e.g. triggered by the gerrit patch submission) and destroyed upon completion\r
+of all functional tests. Each node is a Virtual Machine and each connection\r
+that is drawn on the diagram is available for use in any test case. During the\r
+test execution, all nodes are reachable thru the Management network connected\r
+to every node via dedicated virtual NICs and virtual links (not shown above\r
+for clarity).\r
+\r
+For the test cases that require DUT (VPP) to communicate with VM over the\r
+vhost-user interfaces, a nested VM is created on SUT1 and/or SUT2 for the\r
+duration of these particular test cases only. DUT (VPP) test topology with VM\r
+is shown in the figure below including the applicable packet flow thru the VM\r
+(marked in the figure with ``***``).\r